Pneumatic tire

ABSTRACT

A pneumatic tire comprising a carcass 11, at least one inclined belt layer 13 having a cord extending inclined at an angle of 30° or more relative to the tire circumferential direction, and a tread 15 arranged outward in the tire radial direction of the inclined belt layer 13, wherein a circumferential cord layer 14 arranged inward in the tire radial direction of the tread 15 has a high-rigidity region and a low-rigidity region and the high-rigidity region has a higher negative ratio in a ground contact width of the tread 15 than the low-rigidity region.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of International Application No.PCT/JP2017/046260 filed Dec. 22, 2017, claiming priority based onJapanese Patent Application No. 2017-069109 filed Mar. 30, 2017.

TECHNICAL FIELD

The present disclosure relates to a pneumatic tire.

BACKGROUND

Tire noise generated by rolling tires while driving a motor vehicle isconsidered to be an aspect of tire performance, and various improvementsfor improving the tire performance have been considered. One of thefactors that generate tire noise is the noise emitted by vibration ofthe tread portion.

Additionally, in recent years, the reduction of the weight of the tirehas been attempted in order to reduce the rolling resistance of thetire, but along with the reduction in weight, the vibration dampingproperty in the rolling tire is reduced, and the noise emission emittedfrom the tire tends to increase.

For example, a pneumatic tire (refer to WO2013/161296 (PTL 1)) whichimproves the noise performance while maintaining the steering stabilityand the rolling resistance performance has been proposed as a means forreducing the noise emission.

CITATION LIST Patent Literature

PTL 1: WO2013/161296

SUMMARY Technical Problem

Under such circumstances, for example, even when the reduction of therolling resistance of the tire was achieved by reducing the weight ofthe tire, a tire capable of more effectively suppressing the noiseemission due to the vibration of the tread portion has been desired.

It would thus be helpful to provide a pneumatic tire in which therolling resistance performance is maintained while suppressing the noiseemission to improve the noise performance.

Solution to Problem

To obtain the aforementioned object, a pneumatic tire according to thepresent disclosure comprises a carcass toroidally extending between apair of bead portions, at least one inclined belt layer arranged passingthrough a tire equator outward in the tire radial direction of a crownportion of the carcass, and having a cord extending inclined at an angleof 30° or more with respect to a tire circumferential direction, and atread arranged outward in the tire radial direction of the inclined beltlayer, wherein at least one circumferential cord layer having a cordextending along the tire circumferential direction is arranged inward inthe tire radial direction of the tread, the circumferential cord layerhaving a high-rigidity region which is a region including the tireequator and in which the rigidity in the tire circumferential directionper unit width in the tire width direction is high, and a low-rigidityregion which is a region on each side in the tire width direction of thehigh-rigidity region and in which the rigidity in the tirecircumferential direction per unit width in the tire width direction islow, and the high-rigidity region has a higher negative ratio in aground contact width of the tread than the low-rigidity region.

A pneumatic tire according to the present disclosure comprises a carcasstoroidally extending between a pair of bead portions, at least oneinclined belt layer arranged outward in the tire radial direction of acrown portion of the carcass and having a cord extending inclinedrelative to the tire circumferential direction, and a tread arrangedoutward in the tire radial direction of the inclined belt layer, whereinat least one circumferential cord layer having a cord extending alongthe tire circumferential direction is arranged inward in the tire radialdirection of the tread, the inclined belt layer includes at least awide-width inclined belt layer having a relatively wide width in thetire width direction and a narrow-width inclined belt layer having arelatively narrow width in the tire width direction, both passingthrough the tire equator, and when an inclination angle relative to thetire circumferential direction of the cord of the wide-width inclinedbelt layer is θ1 and an inclination angle relative to the tirecircumferential direction of the cord of the narrow-width inclined beltlayer is θ2, 30°≤θ1≤85°, 10°≤θ2≤30°, and, θ1>θ2 are satisfied, theinclined belt layer has a high-rigidity region which is a regionincluding the tire equator and in which the rigidity in the tirecircumferential direction per unit width in the tire width direction ishigh, and a low-rigidity region which is a region on each side in thetire width direction of the high-rigidity region and in which therigidity in the tire circumferential direction per unit width in thetire width direction is low, and the high-rigidity region has a highernegative ratio in a ground contact width of the tread than thelow-rigidity region.

In the description, the above-mentioned width in the tire widthdirection and the like, unless stated otherwise, shall be measured bymounting a tire on an applicable rim, filling the prescribed internalpressure, and under no load.

The “applicable rim” is an approved rim (“measuring rim” in the ETRTOStandards Manual and “design rim” in the IRA Year Book) prescribed inthe following standards in accordance with a tire size, the “prescribedinternal pressure” is the air pressure prescribed in the followingstandards corresponding to the maximum load capability, and the “maximumload capability” is the maximum mass which is allowed to be loaded on atire by the following standards. Moreover, the standard is an effectiveindustrial standard in areas where tires are produced or used, asdescribed in the Japan Automobile Tyre Manufacturers Association (JATMA)Year Book in Japan, the European Tyre and Rim Technical Organisation(ETRTO) Standards Manual in Europe, or the Tire and Rim Association(TRA) Year Book in the United States.

Further, the state “extending along the ire circumferential direction”includes the case when the cord is parallel to the tire circumferentialdirection, and the case when the cord is somewhat inclined with respectto the tire circumferential direction (the case when the angle withrespect to the tire circumferential direction is approximately 5° orless).

Furthermore, “the ground contact width of the tread” indicates themaximum width of a surface where the tire surface comes into contactwith the ground in a state in which the maximum load (maximum loadcapability) and the air pressure corresponding to the maximum load isapplied, that is, the maximum straight distance in the tread widthdirection of the tread surface. The “negative ratio” indicates the ratioof the area of the groove with respect to the area of the tread surface.

Advantageous Effect

The present disclosure can provide a pneumatic tire in which the rollingresistance performance is maintained while suppressing the noiseemission and improving the noise performance.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings,

FIG. 1A is a schematic view of a pneumatic tire according to a firstembodiment of the present disclosure, and is a cross-sectional view inthe tire width direction of the whole tire, and FIG. 1B is a plan viewof the layer structure in the tread portion of FIG. 1A.

FIG. 2 is a schematic view of another example of the pneumatic tire ofFIG. 1, and is a plan view of the layer structure in the tread portion.

FIG. 3A is a schematic view of a pneumatic tire according to a secondembodiment of the present disclosure, and is a plan view of the layerstructure in the tread portion, and FIG. 3B is a plan view similar toFIG. 3A illustrating another example of the pneumatic tire.

DETAILED DESCRIPTION

An embodiment of the present disclosure will be described below usingthe drawings in accordance with need.

FIRST EMBODIMENT

As illustrated in FIGS. 1A and 1B, a pneumatic tire 10 according to afirst embodiment of the present disclosure (hereinafter, also referredto simply as the “tire”) comprises a carcass 12 toroidally extendingbetween a pair of bead portions 11, an inclined belt layer 13 which isarranged outward in the tire radial direction of a crown portion of thecarcass 12, a circumferential cord layer 14, and a tread 15 arrangedoutward in the tire radial direction of the inclined belt layer 13. Thepneumatic tire 10 is used by mounting on a motor vehicle, and isparticularly suitable as the pneumatic tire for passenger vehicles.

Note that, the circumferential cord layer 14 is arranged inward in thetire radial direction of the tread 15, and may be arranged outward inthe tire radial direction relative to the inclined belt layer 13, orinward in the tire radial direction relative to the inclined belt layer13.

The inclined belt layer 13 has a cord extending inclined relative to thetire circumferential direction, and comprises at least one layerarranged through a tire equator CL; in the present embodiment, only twolayers of a wide-width inclined belt layer 13 a having a relatively widewidth in the tire width direction and a narrow-width inclined belt layer13 b having a relatively narrow width in the tire width direction whichform an intersecting layer. Herein, it is preferable that at least thetire width direction center of the wide-width inclined belt layer 13 acoincides with the tire equator CL, in the present embodiment, the tirewidth direction centers of the wide-width inclined belt layer 13 a andthe narrow-width inclined belt layer 13 b coincide with the tire equatorCL.

The width of a maximum width inclined belt layer (in the presentembodiment, the wide-width inclined belt layer 13 a) which has thewidest width in the inclined belt layer 13 is set to 90% to 115% of thewidth in the tire width direction (tread width) of the tread 15,preferably 100% to 105% (in the present embodiment, 105%).

The inclination angle of the cords of the inclined belt layer 13 withrespect to the tire circumferential direction is from 30° to 90°,preferably from 50° to 75°. If the inclination angle of the cords of theinclined belt layer 13 with respect to the tire circumferentialdirection is less than 30°, the rigidity with respect to the tire widthdirection decreases, thus, the steering stability especially uponcornering cannot be adequately obtained, and shearing deformation of therubber between layers increases, and accordingly, the rolling resistanceperformance deteriorates. Further, the steering stability and therolling resistance performance can be maintained at a high level bysetting the inclination angle of the cords of the inclined belt layer 13with respect to the tire circumferential direction to 50° or more.

A metal cord and in particular, a steel cord can be used as the materialof the cord of the inclined belt layer 13, but it is also possible touse an organic fiber cord (in the present embodiment, a steel cord). Thesteel cord may include steel as a main component, and can also containvarious micro inclusions such as carbon, manganese, silicon,phosphorous, sulfur, copper, and chromium. Further, a monofilament cordand cords obtained by twisting a plurality of filaments can be used, andvarious designs may be adopted for the twist structure, which may bedifferent in, for example, sectional structure, twist pitch, twistdirection, and/or distance of adjacent filaments. Furthermore, cordsobtained by twisting filaments of different materials may also be used,which may employ various twist structures such as single twist, layertwist, and multi twist without being limited to any particular sectionalstructure.

The number of cords implanted is, for example, set to a range of 20 to60 cords/50 mm, but it is not limited to this range. Further, thewide-width inclined belt layer 13 a and the narrow-width inclined beltlayer 13 b may have the same or a different number of such cords.

The circumferential cord layer 14 has a cord extending along the tirecircumferential direction, and at least one layer; in the presentembodiment, the two layers of the wide-width circumferential cord 14 ahaving a relatively wide width in the tire width direction and thenarrow-width circumferential cord layer 14 b having a relatively narrowwidth in the tire width direction, is arranged outward in the tireradial direction relative to the inclined belt layer 13. Herein, atleast, it is preferable that the tire width direction center of thewide-width circumferential cord layer 14 a be coincident with the tireequator CL, and in the present embodiment, the tire width directioncenters of the wide-width circumferential cord layer 14 a and thenarrow-width circumferential cord layer 14 b coincide with the tireequator CL. Therefore, in the present embodiment, the inclined beltlayer 13 (in the present embodiment, the wide-width inclined belt layer13 a and the narrow-width inclined belt layer 13 b) and thecircumferential cord layer 14 (in the present embodiment, the wide-widthcircumferential cord layer 14 a and the narrow-width circumferentialcord layer 14 b) are arranged symmetrically in a pair of tire halveswhich sandwich the tire equator CL in the tire width direction.

In the present embodiment, the narrow-width circumferential cord layer14 b has a width in the tire width direction which is about 0.5 timesthe width in the tire width direction of the wide-width circumferentialcord layer 14 a which is the maximum width in the tire width directionof the circumferential cord layer 14, and the wide-width circumferentialcord layer 14 a and the narrow-width circumferential cord layer 14 bboth have their tire width direction centers arranged on the tireequator CL (refer to FIGS. 1 A and 1B). Therefore, the circumferentialcord layer 14 has a center region which is the center portion of thewidth in the tire width direction which includes at least the tireequator CL as a two layer structure of the wide-width circumferentialcord layer 14 a and the narrow-width circumferential cord layer 14 b,and makes the rigidity in the tire circumferential direction of anyportion of the center region higher than the rigidity in the tirecircumferential direction of any portion of both shoulder regionsadjacent to the center region.

Namely, the circumferential cord layer 14 has a high-rigidity region (inthe present embodiment, the region in which the wide-widthcircumferential cord layer 14 a overlaps with the narrow-widthcircumferential cord layer 14 b) which is a region including the tireequator CL and in which the rigidity in the tire circumferentialdirection per unit width in the tire width direction is high, and alow-rigidity region which is a region on each side in the tire widthdirection of the high-rigidity region and in which the rigidity in thetire circumferential direction per unit width in the tire widthdirection is low (in the present embodiment, the region of only thewide-width circumferential cord layer 14 a and in which the wide-widthcircumferential cord layer 14 a and the narrow-width circumferentialcord layer 14 b do not overlap with each other).

This high-rigidity region, other than forming by increasing the number(number of layers) of circumferential cord layers 14 relative to thelow-rigidity region, can also be formed by changing the type of cords inthe high-rigidity region and the low-rigidity region, but it ispreferable to form the entire circumferential cord layer 14 as the samemember by increasing the number of circumferential cord layers 14 in thehigh-rigidity region relative to the number of circumferential cordlayers 14 in the low-rigidity region.

Even among tires for passenger vehicles, in a tire having a largeinclination angle (for example, 30° or more) of the cord of the inclinedbelt layer with respect to the tire circumferential direction, in a highfrequency region of 400 Hz to 2 kHz, the tread surface tends to have ashape that largely vibrates uniformly in primary, secondary, tertiary,etc., vibration modes in a sectional direction, and thus, a large noiseemission is generated. Therefore, locally increasing the rigidity in thecircumferential direction of the width direction central portion of thetread, makes the width direction central portion of the tread lesslikely to expand in the tire radial direction, and thus, the noiseemission is reduced.

The circumferential cord layer 14 preferably has a high rigidity, andmore specifically, comprises a rubberized layer of cords extending inthe tire circumferential direction, and preferably satisfies 1500≥X≥750where X is defined as X=Y×n×m×d, Y is the Young's modulus (GPa) of thecords, n is the number of cords implanted (cords/50 mm), in is thenumber of circumferential cord layers 14, and d is the cord diameter(mm).

Note that, the cord diameter d is preferably 0.5 to 1.2 mm.

In the present embodiment, the tire width direction end of thecircumferential cord layer 14 is preferably arranged on the outer sidein the tire width direction relative to the tire width direction end ofthe narrow-width inclined belt layer 13 b, and, on the inner side in thetire width direction relative to the tire width direction end of thewide-width inclined belt layer 13 a.

Further, wavy-shaped cords may be used in the circumferential cord layer14 in order to increase the rupture strength. A high-elongation cord(for example, with an elongation at break of 4.5% to 5.5%) may be usedto increase the rupture strength in the same manner. Various materialswhich may be adopted as the cord material, and typical examples includerayon, nylon, polyethylene naphthalate (PEN), polyethylene terephthalate(PET), aramid, glass fiber, carbon fiber, and steel. In terms of weightreduction, an organic fiber cord is particularly preferable.

The cord can use monofilament cords, cords obtained by twisting aplurality of filaments, or hybrid cords obtained by twisting filamentsof different materials. The number of cords implanted is set to a rangeof 20 to 60 cords/50 mm, but it is not limited to this range.

The circumferential cord layer 14 can be designed to have a wider ornarrower width in the tire width direction than the inclined belt 13,and for example, the width can be set to 90 to 110% of the maximum widthinclined belt layer (in the present embodiment, the wide-width inclinedbelt layer 13 a) having the largest width in the tire width direction inthe inclined belt 13.

Further, from the production standpoint, it is particularly advantageousto configure the circumferential cord layer 14 as a spiral layer, butthe layer may be formed by spirally winding a striped cord in which aplurality of core wires arranged in parallel with each other on a planeare bundled together by a wrapping wire with the parallel arrangementbeing maintained.

The tread 15 is set so that the high-rigidity region (in the presentembodiment, the region in which the wide-width circumferential cordlayer 14 a overlaps with the narrow-width circumferential cord layer 14b) of the circumferential cord layer 14 has a higher negative ratio inthe ground contact width of the tread than the low-rigidity region (inthe present embodiment, the region of only the wide-widthcircumferential cord layer 14 a) of the circumferential cord layer 14.The rigidity balance of the tread surface can be maintained thereby,thus, the deterioration of the uneven wear performance due to thedeterioration of the ground contact area can be suppressed.

The pattern of the tread 15 may be either of a pattern symmetrical inthe tire width direction about the tire equator CL or an asymmetricpattern. The negative ratio of the pattern can be set to, for example,30% or less. When a circumferential main groove is provided in the tread15, 2 to 4 grooves are preferable, and the groove width of thecircumferential main groove is preferably in the range of about 4 to 10mm. Note that, there does not have to be a circumferential main groove,and it may be a rib-like land portion or a block-like land portion.

The tread rubber which configures the tread 15 may be formed by aCAP/BASE structure, having a plurality of different types of rubberlayers in the tire radial direction. The plurality of rubber layers maybe different in tangent loss, modulus, hardness, glass transitiontemperature, material, or the like. Further, the ratio of the thicknessin the tire width direction of the plurality of rubber layers may varyin the tire width direction. Moreover, for example, a rubber layerdifferent from its surroundings may be provided only at thecircumferential main groove bottom.

Further, the tread rubber may be formed of a divided tread structureconsisting of a plurality of different types of rubber layers in thetire width direction. The plurality of rubber layers may be different intangent loss, modulus, hardness, glass transition temperature, material,or the like. Further, the ratio of the length in the tire widthdirection of the plurality of rubber layers in the tire width directionmay vary in the tire radial direction. Further, a rubber layer differentfrom its surroundings may be provided only in a limited region such asnear the circumferential main groove, near the tread edge, on theshoulder land portion, or on the center land portion.

In the pneumatic tire 10 according to the present disclosure, variousstructures in the pneumatic tire can be adopted in a carcass line whichis an extended ring portion of the carcass 12 in the tire widthwisesection, for example, the maximum width position of the carcass in thetire radial direction may be close to the bead portion side or may beclose to the tread side. As an example, the maximum width position ofthe carcass may be in a range of 50% to 90%, in a tire height ratio, onthe outer side in the tire radial direction from the bead base portion.The number of cords of the carcass implanted can also adopt variousstructures in the pneumatic tire, and for example, is preferably 20 to60 cords/50 mm, but it is not limited to this range. Further, the cordarrangement in the carcass may be a bias structure or may be a radialstructure (in the present embodiment, a radial structure is adopted).

A carcass folded-up portion in which the carcass 12 folds up the beadcore of the bead portion 11 can also adopt various structures in thepneumatic tire, for example, a folded-up end of the carcass 12 can bearranged inward in the tire radial direction relative to the bead fillerend, and further, the carcass folded-up end can be stretched to theouter side in the tire radial direction relative to the bead filler endand the tire maximum width position, and can be stretched, in somecases, to the inner side in the tire width direction relative to thetire width direction end of the belt layer. Furthermore, when thecarcass 12 is comprised of a plurality of carcass layers, the tireradial direction positions of the carcass folded-up ends can bedifferent. Further, the carcass folded-up portion may not be present inthe first place, and instead, the carcass may adopt a structuresandwiched between a plurality of bead core members or wound around thebead core.

In the tire side portion, the tire maximum width position may be in arange of 50% to 90%, in a tire height ratio, on the outer side in thetire radial direction from the bead base portion, Further, it can alsobe a structure having a rim guard.

Further, it can also be a structure without the bead filler.

The bead core can adopt various structures in the pneumatic tire such asa circular shape and a polygonal shape, and further, as stated above,other than the structure in which the carcass is wound around the beadcore, a structure in which the bead core is divided so as to sandwichthe carcass by a plurality of bead core members is possible. Further, inorder to reinforce the bead core surroundings, a rubber layer, a cordlayer and the like can be provided in the bead portion for the purposeof reinforcement. Such additional members can be provided in variouspositions relative to the carcass and the bead filler.

The air permeation coefficient of the rubber composition constituting aninner liner arranged on the tire inner surface is preferably set to1.0×10⁻¹⁴ cc·cm/(cm²·s·cm Hg) to 6.5×10⁻¹⁰ cc·cm/(cm²·s·cm Hg). Forexample, it is preferable that the inner liner is a rubber layer mainlymade of butyl rubber (in the present embodiment, butyl rubber). Notethat, in addition to the rubber layer mainly made of butyl rubber, theinner liner may be formed with a film layer mainly made of resin.

Further, the tire inner surface may be provided with a porous member (asponge or the like), or subjected to electrostatic flocking processing,for reducing cavity resonance noise, or provided with a sealant memberfor preventing air leakage upon puncture.

Further, the pneumatic tire may be a side-reinforced run-flat tireincluding a reinforcing rubber having a crescent-shaped cross section inthe tire side portion.

In the pneumatic tire 10, the circumferential cord layer 14 may bearranged asymmetrically relative to the tire equator CL.

As illustrated in FIG. 2, in the present embodiment, the pneumatic tire20, in addition to the circumferential cord layer 14 beingasymmetrically arranged relative to the tire equator CL, has the samestructure and operation as the pneumatic tire 10 according to theaforementioned first embodiment.

In the pneumatic tire 20, the wide-width circumferential cord layer 14 aand the narrow-width circumferential cord layer 14 b are formed so thatwhen W1 denotes the width in the tire width direction (in the presentembodiment, the width in the tire width direction of the wide-widthcircumferential cord layer 14 a) of the entire circumferential cordlayer 14, W2 denotes the width in the tire width direction (in thepresent embodiment, the width in the tire width direction of thenarrow-width circumferential cord layer 14 b) of the high-rigidityregion (in the present embodiment, the region in which the wide-widthcircumferential cord layer 14 a overlaps with the narrow-widthcircumferential cord layer 14 b), and D1 and D2 respectively denote thelonger and the shorter among the distances in the tire width directionfrom each end in the tire width direction of the entire circumferentialcord layer 14 to each end in the tire width direction of thehigh-rigidity region on a side close to each end in the tire widthdirection of the circumferential cord layer 14 (in the presentembodiment, the narrow-width circumferential cord layer 14 b),W2/W1=0.2 to 0.7, and, D1/D2=2.0 to 8.0 are satisfied.

Namely, in the pneumatic tire 20, the center region (in the presentembodiment, the region in which the wide-width circumferential cordlayer 14 a overlaps with the narrow-width circumferential cord layer 14b) of the circumferential cord layer 14 which is the high-rigidityregion is extended over a range from 0.2 times to 0.7 times the maximumwidth W in the tire width direction of the circumferential cord layer14, and furthermore, comprises a structure in which the widths D1 and D2in tire width direction of each shoulder region (in the presentembodiment, the region of only the wide-width circumferential cord layer14 a) which is the low-rigidity region of the circumferential cord layer14 are different where the ratio D1/D2 is in a range from 2.0 to 8.0,that is, the circumferential cord layer 14 is arranged asymmetricallywith respect to the tire equator CL as seen in the tire widthwisesection (in the present embodiment, shifted rightward in the drawing(refer to FIG. 2)). Therefore, not only is the amplitude of thevibration mode which causes the noise emission suppressed, but thevibration mode is separated into two vibration modes. As a result, thepeak level of the sound is reduced more effectively, thus, it ispossible to further reduce the noise emission generated from the tire.

In this way, the noise emission generated from the tire can be reducedin the pneumatic tire 20 in which the peak level of sound is reduced bydecreasing the amplitude of the vibration generated in the tire andseparating the amplitude into different modes regardless of other tireconfigurations, for example, the size of the cord angle of the inclinedbelt layer.

Third Embodiment

A pneumatic tire 30 according to a third embodiment of the presentdisclosure comprises, as illustrated in FIG. 3A, an inclined belt layer31 including at least a wide-width inclined belt layer 31 a having arelatively wide width in the tire width direction and a narrow-widthinclined belt layer 31 b having a relatively narrow width in the tirewidth direction, both passing through the tire equator CL, and when theinclination angle with respect to the tire circumferential direction ofthe cord of the wide-width inclined belt layer 31 a is θ1, and theinclination angle with respect to the tire circumferential direction ofthe cord of the narrow-width inclined belt layer 31 b is θ2, 30°≤θ1≤85°,10°≤θ2≤30°, and θ1>θ2 are satisfied. The other structures and operationsare the same as the pneumatic tire 10 according to the aforementionedfirst embodiment.

In the present embodiment, the narrow-width inclined belt layer 31 b ofthe pneumatic tire 30 has a width in the tire width direction which isabout 0.5 times the width in the tire width direction of the wide-widthinclined belt layer 31 a which is the tire width direction maximum widthof the inclined belt layer 31, and the wide-width inclined belt layer 31a and the narrow-width inclined belt layer 31 b both have their tirewidth direction centers arranged at the tire equator CL (refer to FIG.3A). Therefore, the inclined belt layer 31 has a center region which isthe center portion of the width in the tire width direction whichincludes at least the tire equator CL as a two layer structure of thewide-width inclined belt layer 31 a and the narrow-width inclined beltlayer 31 b, and makes the rigidity in the tire circumferential directionof any portion of the center region higher than the rigidity in the tirecircumferential direction of any portion of both shoulder regionsadjacent to the center region.

If the inclination angle θ1 with respect to the tire circumferentialdirection of the cord forming the wide-width inclined belt layer 31 a is30° or more, the circumferential elongation of rubber increases as thesurface of the tread 15 deforms, thus, the ground contact length of thetire is sufficiently maintained. As a result, the cornering power canincrease to achieve a high turning performance. Note that, if theinclination angle θ1 exceeds 85°, there is the risk that thecircumferential bending rigidity may become excessively small, thus, theinclination angle θ1 is set to 85° or less.

However, when the inclination angle θ1 of the cord of the inclined beltlayer 31 a having the widest width is made too large, the vibration modeof the tire changes, and accordingly, a noise emission is generated, andthe noise performance tends to deteriorate. In more detail, in a highfrequency region of 400 Hz to 2 kHz, the tread surface of many tireshaving the cord of the inclined belt layer inclined at about 30° to 85°with respect to the tire circumferential direction have a shape thatlargely vibrates uniformly in primary, secondary, tertiary, etc.vibration modes in a sectional direction, and thus, there is the fearthat a large noise emission is generated.

Therefore, if the inclination angle θ2 of the cord of the narrow-widthinclined belt layer 31 b relative to the tire circumferential directionis set to be smaller than the inclination angle θ1 of the cord of thewide-width inclined belt layer 31 a, and is in the range of 10° to 30°,the out-of-plane bending stiffness in the tire circumferential directionis appropriately maintained in the vicinity of the tire equator CL,thus, the vibration of the tread surface can be suppressed in theaforementioned vibration modes. That is, the expansion of the tread 15in the tire circumferential direction in the vicinity of the tireequator CL is suppressed, and as a result, such noise emission can befurther decreased.

By the inclination angle θ2 being set to 10° or more, the out-of-planebending stiffness in the tire circumferential direction can bemaintained in the wide-width inclined belt layer 31 a without inhibitingthe operation for maintaining the ground contact length, and by settingthe inclination angle θ2 to 30° or less, the out-of-plane bendingstiffness of the tire circumferential direction is appropriatelymaintained in the vicinity of the tire equator CL, thus, the generationof noise emission can be more reliably decreased.

In addition, the pneumatic tire 30 of the present embodiment isconfigured so that the high-rigidity region (in the present embodiment,the region in which the wide-width inclined belt layer 31 a and thenarrow-width inclined belt layer 31 b overlap with each other) of theinclined belt layer 31 has a higher negative ratio in the ground contactwidth of the tread 15 than the low-rigidity region (in the presentembodiment, the region of only the wide-width inclined belt layer 31 a)of the inclined belt layer 31. As a result, the dampening of thevibration mode is further improved and the noise performance can befurther improved.

In the pneumatic tire 30, the inclined belt layer 31 may be arrangedasymmetrically relative to the tire equator CL.

As illustrated in FIG. 3B, in the present embodiment, the pneumatic tire40, other than the inclined belt layer 31 being arranged asymmetricallywith respect to the tire equator CL, has the same structure andoperation as the aforementioned pneumatic tire 30.

In the pneumatic tire 40, the wide-width inclined belt layer 31 a andthe narrow-width inclined belt layer 31 b are formed so that when W1denotes the width in the tire width direction of a widest-width inclinedbelt layer having the widest width in the tire width direction in theinclined belt layer 31 (in the present embodiment, the width in the tirewidth direction of the wide-width inclined belt layer 31 a). W2 denotesthe width in the tire width direction of a narrowest-width inclined beltlayer having the narrowest width in the tire width direction in theinclined belt layer 31 (in the present embodiment, the width in the tirewidth direction of the narrow-width inclined belt layer 31 b), and D1and D2 respectively denote the longer and the shorter among thedistances in the tire width direction from each end in the tire widthdirection of the entire inclined belt layer 31 to each end in the tirewidth direction of the narrowest-width inclined belt layer (in thepresent embodiment, the narrow-width inclined belt layer 31 b) on a sideclose to each end in the tire width direction of the widest-widthinclined belt layer (in the present embodiment, the wide-width inclinedbelt layer 31 a),W2/W1=0.2 to 0.7, and, D1/D2=2.0 to 8.0 are satisfied.

Namely, in the pneumatic tire 40, the center region (in the presentembodiment, the region in which the wide-width inclined belt layer 31 aand the narrow-width inclined belt layer 31 b overlap with each other)of the inclined belt layer 31 which is the high-rigidity region isextended over a range from 0.2 times to 0.7 times the maximum width W inthe tire width direction of the inclined belt layer 31, and furthermore,comprises a structure in which the widths D1 and D2 in the tire widthdirection of each shoulder region (in the present embodiment, the regionof only the wide-width inclined belt layer 31 a) which is thelow-rigidity region of the inclined belt layer 31 are different wherethe ratio D1/D2 is in a range from 2.0 to 8.0, that is, the inclinedbelt layer 31 is arranged asymmetrically with respect to the tireequator CL as seen in the tire widthwise section (in the presentembodiment, shifted rightward in the drawing (refer to FIG. 3B)).Therefore, not only is the amplitude of the vibration mode which causesthe noise emission suppressed, but the vibration mode is separated intotwo vibration modes. As a result, the peak level of the sound is reducedmore effectively, thus, it is possible to further reduce the noiseemission generated from the tire.

In this way, the noise emission generated from the tire can be reducedin the pneumatic tire 10 in which the peak level of sound is reduced bydecreasing the amplitude of the vibration generated in the tire andseparating the amplitude into different modes regardless of other tireconfigurations, for example, the size of the cord angle of the inclinedbelt layer.

In the present disclosure, when the tire internal pressure is set to 250kPa or more, the sectional width SW and the outer diameter OD of thetire preferably satisfy the relational expression:OD≥−0.0187×SW²+9.15×SW−380. The reason is that the drag coefficient (Cdvalue) and the rolling resistance value (RR value) can be reduced toimprove the fuel efficiency. Further, the tire is preferably used as apassenger vehicle pneumatic radial tire.

REFERENCE SIGNS LIST

10, 20, 30, 40 . . . pneumatic tire,

11 . . . bead portion,

12 . . . carcass,

13, 31 . . . inclined belt layer,

13 a, 31 a . . . wide-width inclined belt layer,

13 b, 31 b, . . . narrow-width inclined belt layer,

14 . . . circumferential cord layer,

14 a, 31 a . . . wide-width circumferential cord layer,

14 b, 31 b . . . narrow-width circumferential cord layer,

15 . . . tread,

CL . . . tire equator

The invention claimed is:
 1. A pneumatic tire comprising: a carcasstoroidally extending between a pair of bead portions, at least oneinclined belt layer arranged outward in a tire radial direction of acrown portion of the carcass and having a cord extending inclinedrelative to a tire circumferential direction, and a tread arrangedoutward in the tire radial direction of the inclined belt layer, one ormore circumferential grooves, and at least one circumferential cordlayer having a cord extending along the tire circumferential directionis arranged inward in the tire radial direction of the tread, whereinthe inclined belt layer includes at least a wide-width inclined beltlayer having a relatively wide width in the tire width direction and anarrow-width inclined belt layer having a relatively narrow width in thetire width direction, both passing through the tire equator, and when aninclination angle relative to the tire circumferential direction of thecord of the wide-width inclined belt layer is θ1 and an inclinationangle relative to the tire circumferential direction of the cord of thenarrow-width inclined belt layer is θ2, 30°≤θ1≤85°, 10°≤θ2≤30°, and, θ1≥θ2 are satisfied, the inclined belt layer has a high-rigidity regionwhich is a region including the tire equator and in which the rigidityin the tire circumferential direction per unit width in the tire widthdirection is high, and a low-rigidity region which is a region on eachside in the tire width direction of the high-rigidity region and inwhich the rigidity in the tire circumferential direction per unit widthin the tire width direction is low, the high-rigidity region has ahigher negative ratio in a ground contact width of the tread than thelow-rigidity region; and a groove width of a circumferential groove,which has a maximum groove width from among all of the one or morecircumferential grooves, is 4 to 10 mm; wherein when W1 denotes a widthin the tire width direction of a widest-width inclined belt layer havingthe widest width in the tire width direction in the inclined belt layer,W2 denotes a width in the tire width direction of a narrowest-widthinclined belt layer having the narrowest width in the tire widthdirection in the inclined belt layer, and D1 and D2 respectively denotethe longer and the shorter among the distances in the tire widthdirection from each end in the tire width direction of the widest-widthinclined belt layer to each end in the tire width direction of thenarrowest-width inclined belt layer on a side close to each end in thetire width direction of the widest-width inclined belt layer, W2/W1=0.2to 0.7, and, D1/D2=2.0 to 8.0 are satisfied.
 2. The pneumatic tireaccording to claim 1, wherein a pattern of the tread has a negativeratio of a pattern of 30% or less, the one or more circumferentialgrooves comprise 2 to 4 circumferential main grooves, and a groove widthof each of the circumferential grooves is in the range of 4 to 10 mm. 3.The pneumatic tire according to claim 1, wherein a number of cords ofthe carcass is 20 to 60 cords/50 mm.
 4. The pneumatic tire according toclaim 1, wherein further comprising an inner liner arranged on a tireinner surface, wherein an air permeation coefficient of a rubbercomposition constituting the inner liner arranged on the tire innersurface is set to 1.0×10-14 cc·cm/(cm2 ·s·cm Hg) to 6.5×10-10 cc·cm/(cm2·s·cm Hg).